Various types of inflatable low pressure elastomeric devices have been used for flotation functions. These devices are commonly employed as life rafts, life jackets or vests and flotation bags. The extreme popularity of such inflatable members can be attributed to the fact that they are extremely lightweight as they can be manufactured of a relatively thin elastomeric membrane. Another advantage of such inflatable members is the fact that they are highly compact in that they can be stored in a deflated condition and inflated with air, carbon dioxide, nitrogen or other gases only in circumstances where they are to be employed. This is particularly significant since most inflatable devices of this type are employed only in emergencies which are normally rare occurrences.
While possessing the above and other highly advantageous traits these inflatable devices do exhibit certain disadvantageous features. One such feature is that in the event a substantial shock or blow is imparted to the inflatable device or in the event of overfill a failure of the material may occur. Such shocks or blows can be accidently imparted as by a person wearing an inflated life jacket or vest falling a substantial distance into water. Overfill may result from overheated inflation containers, overly high storage pressure, manual fill followed by automatic fill, or other improper operating procedure. The attendant shock or rapid collapse of the inflatable member can cause a rupture of the material itself, a failure at a seam joining pieces of material, a failure at a joint as where an inflating stem or other member may be attached to the inflatable member or more insidiously, an overstress which can lead to premature failure at a later time. In order to obviate the possibly disastrous results of such shock induced failures, such inflatable members are normally provided with a pressure relief device.
Pressure relief devices have been developed which are in the nature of a fitting which is attached to the inflatable member and which operates as a relief valve. While the inflatable members are capable of extended trouble-free operation at their designed pressure of approximately one to five psi, the relief valve must be capable of instantaneously venting fluid in the event that there is a gradual pressure overfill or a sudden shock induced pressure increase before failure of the inflatable member is induced. In addition to the requirement that the pressure relief cartridge permit rapid escape of fluid under shock loading, it is also essential that it be capable of rapidly closing after excess pressure has been vented or relieved in order to permit continuing safe operation of the inflatable member in a still inflated condition possessing much of the inflating fluid which is normally contained.
In most instances, pressure relief devices have consisted of relatively large metallic valves. In general, the valves consist of a heavy brass housing which encloses a floating diaphragm or poppet-tupe valve element. Normally, the inflatable members have a substantially rigid elastomeric member peripherally encompassing a hole in the inflatable member with the elastomer interfitting in a U-shaped peripheral groove in the relief cartridge housing which is swaged or bonded into sealing engagement with the elastomer. Such pressure relief cartridges in employing floating diaphragm or poppet elements normally have in the instance of diaphragms flat elastomeric sealing surfaces which are characteristically capable of only limited compression to effect sealing. In the case of poppet elements circular or O-ring sealing members are commonly employed; however, these sealing members also exhibit minimal compression and quickly become stiff upon compression resulting in diminished long-term sealing capability. As a result of the limited compression capabilities of these sealing devices, difficulties in obtaining repeatedly good seals have frequently been encountered in instances where there may be slight misalignment of the operating components, where they may be slight errors in component tolerances or where contamination or foreign material may reside on the seals or the seal engaging surfaces. In this respect it is to be appreciated that with the low pressures on the order of one or two psi normally present internally of the inflatable member and somewhat higher pressures existing when a relief valve is seating, the valve sealing elements receive substantially no assistance in seating or unseating from the operating pressure of the fluids.
An approach to achieving the objective of positive accurate sealing upon closure of the valve element is to employ sealing members of softer more pliable elastomeric materials. However, the use of softer, more pliable sealing materials inevitably results in increased probabilities of sticking or erratic adhesion between the sealing member and its seating surface thereby producing the possibilities of erratic or delayed opening of the valve which can result in an overstress or failure of the inflatable member. For the above and other reasons existing pressure relief cartridges for such inflatable members have characteristically encountered severe reliability problems which has necessitated frequent servicing and/or replacement of these pressure relief cartridges. In addition, many of the devices are not replaceable such that if they fail to meet operational test parameters the entire inflatable member must be discarded. Also, the existing devices normally are not pressure adjustable in that the tolerances of the operating parts must be relied upon exclusively to achieve the pressure relief tolerances for the device. Therefore, both the operating and replacement considerations involving existent pressure relief devices have proven to be less than satisfactory considering the critical function which these devices perform.